Borane which is a hydrogen compound of boron is a compound that forms a three-centered two-electron bond using an unoccupied orbital of boron and, in view of its feature, is stabilized by dimerization or formation of a complex with a Lewis basic material. Further, since borane is highly reducing, it acts as a reducing agent, for example, to an unsaturated bond in organic synthesis. In particular, addition reaction to the unsaturated bond is referred to as hydroboration and generally known as a customary method of hydroxylation or coupling reaction.
Further, it has been known that an alkyl borane as a sort of borane compounds generates radicals in a low temperature and oxygen atmosphere and is used also as an initiator for radical polymerization. For example, a method of polymerizing an acrylic monomer using 9-borabicyclo[3,3,1]nonane (9-BBN) as a polymerization initiator (Patent Literature 1) and a method of polymerizing a vinyl compound excluding vinyl acetate using S-alpineborane as a polymerization initiator (Patent Literature 2) are shown. Any of the methods shows a result that a polymerization terminal radical forms dormant species with an alkylborane by using the alkylborane to develop a living radical property. In view of the above, radical polymerization can be performed under excellent polymerization controllability by using an alkylborane type polymerization initiator.
Further, Patent Literature 3 discloses a method of polymerization using borane BH3 as a polymerization initiator for vinylic monomers, and using a complex of BH3 and tetrafuran or a trialkylboron compound under the co-existence of a solvent having etheric oxygen atoms such as tetrahydrofuran, diglyme, dioxane, etc. in the molecular structure thereof in an atmosphere containing 20±5% oxygen, particularly, in atmospheric air.